1. Field of the Invention
The invention relates to a plant and a process for purifying marine diesel exhausts of fine dust particles, and also of certain flue gases.
2. Description of Related Art
The operation of ships, in particular of large ships, as are generally conventional in container shipping, customarily proceeds using heavy oil as a fuel of the marine diesel engines. This takes place against the background that the prices and availability of such heavy oil are significantly lower than those of refined types of motive power fuel.
Such heavy oils are generally also called “marine residual oil”, since they are predominantly obtained from residues of petroleum processing.
In this case residue means that these components are formed as a no longer volatile part of a petroleum-processing process.
The main components of marine residual oil are predominantly alkanes, alkenes, cycloalkanes and highly condensed aromatic hydrocarbons (asphaltenes) having about 20 to 70 carbon atoms per molecule and a boiling range between 300° C. and about 700° C.
In addition, aliphatic and also heterocyclic nitrogen and sulphur compounds are also present in marine residual oils. Customarily the marine residual oils have a nitrogen content of at least 0.5% by weight and a sulphur content of up to 6% by weight. The sulphur content of the residual oils customary in the operation of ships is in the range from 3.5% by weight to 4.5% by weight. In such residual oils, furthermore, all metallic impurities of the petroleum such as nickel, vanadium, sodium, calcium and others are concentrated. Compared with the marine residual oils, diesel power fuels, as are permitted for combustion in cars or lorries in Germany, have a sulphur content of a maximum of 0.001% by weight (10 ppm).
For some time there has existed an International Convention for the Prevention of Pollution from Ships (MARPOL). Since 19 May 2005 this convention also comprises a guideline which regulates the emission of exhausts by ships.
In particular, limiting values are established herein for emitted nitrogen oxides and sulphur oxides for certain sea areas. Compliance with the limiting values is monitored by a multiplicity of national and international shipping authorities and infringement of the regulations is punished with substantial fines.
Currently the ships' owners are therefore forced to change over to comparatively expensive reduced-sulphur motive power fuels since alternatives to these are not available in the maritime sector.
On the other hand, flue gas purification and, in particular, flue gas desulphurization has in the interim become a known technology in the context of operating chemical process plants. However, such devices and processes are customarily plants and processes of considerable size, the adaptation of which to the use for purifying marine diesel exhausts is not readily possible, since on ships the existing space must continue to be available as freight space and since operation in a complex interconnected process as is customary in chemical process plants is not possible.
A process and a device for wet purification of crude gas streams is described for instance in DE 198 32 174 C1. DE 198 32 174 C1 describes that the wet dedusting of dust-laden exhaust and also separating off SO2 and other gaseous components from exhausts is made possible by means of the device and the process carried out in the device.
DE 198 32 174 C1 also describes a plant comprising what is termed a venturi scrubber having a certain nozzle having feed lines for a crude gas and a scrubbing liquid, and also an outlet line for the dust-laden scrubbing liquid together with the purified gas. The outlet line for the dust-laden scrubbing liquid and the purified gas is at the same time a feed line to a cyclone in which the dust-laden scrubbing liquid is thickened and from which the thickened scrubbing liquid is removed from the plant via a first outlet line. Via a second outlet line of the cyclone, which at the same time is a feed line to a rotary scrubber, the remaining residual stream essentially comprising the purified gas is fed to the rotary scrubber. In the rotary scrubber, according to DE 198 32 174 C1 the remaining fractions of the dust are separated off from the purified gas and the very pure gas stream is then removed from the plant via an outlet line of the rotary scrubber.
DE 198 32 174 C1 does not disclose a plant or a process which permits further purification of the scrubbing liquid by means of disc separation devices. Accordingly, the device and the process according to DE 198 32 174 C1 may not enable fractionation of the various components of the crude gas introduced. In addition, DE 198 32 174 C1 does not disclose that the described plant may be usable for purifying marine diesel exhausts or that the disclosed process could find use here.
DE 43 31 301 C2 describes a device for purifying exhausts which, according to DE 43 31 301 C2, differs from devices of similar type otherwise known from the prior art by a reduced space requirement.
DE 43 31 301 C2 does not disclose further devices connected to the device described there, said further devices being for treating the scrubbing liquid used in the device. Accordingly, the device according to DE 43 31 301 C2 likewise may not enable fractionation of the various components of the introduced crude gas. Furthermore, DE 43 31 301 C2 does not disclose that the disclosed device would be usable for purifying marine diesel exhausts.
Against the background of the prior art, the object is therefore to provide a plant and a process which enable marine diesel exhausts from the combustion of heavy oils to be purified and fractionated in such a manner that the ships can continue to be fuelled by heavy oil, but the operation does not infringe the valid provisions with respect to the exhaust limiting values. The above-described fractionation must be implemented such that the highest possible part of the fractions can be introduced back into the surrounding such seawater even during the operation of the ship.